Remote control system



G. w. BAUGHMAN REMOTE CONTROL SYSTEM July 15, l9 41.

Filed Jan. 16, 1940 www@ HIS ATTORNEY x mw o mw If glad mw a. Mlm ML y um x e Mm m u m Y 1.,- .www SS E@ 0 a w ,D I @www Patented July 15, 1941 (ci. 17e-sf 23 Claims.

My invention relates to remote control systems, and more particularly, to the communication or line circuits for centralized traffic control systems for railroads, in which a train dispatchers ofce or other suitable point of control vis connected with a plurality of eld stations by line wires, over which impulse codes of signals are transmitted at times for controlling selected devices at the stations, and at other times f or indicating the condition of station devices at the oice.

My invention is an improvement upon the system disclosed in the copending application Serial No. 600,786, filed March 23, 1932, by L. V. Lewis, for Remote control systems, which corresponds with British Patent No. 415,787, issued September 3, 1934, upon those disclosed in applications Serial Nos. 222,860, filed August 3, 1933, and 223,287, iiled August 5, 1938, by C. S. Snavely and A. B. Miller, for Remote control systems, upon that disclosed in application Serial No, 261,241, filed March 11, 1939, by L. V. Lewis, for Remote control systems, and upon that disclosed in my application, Serial No. 256,976, filed February 17, 1939, for Remote control system.

Since a dispatchers telephone circuit is generally required in connection with systems of this character, it is often desirable to provide additional communication channels over the line' wires of the centralized traffic control system for telephone or telegraph communication, and to also arrange the apparatus so as to permit the use of the line wires by another code system employing diierent codes, such as a dispatchers telephone selector system, without interference, even though two or more codes are initiated simultaneously.`

In order to use the line wires more eiliciently, the dispatchers telephone circuits are usually simplexed, that is, are so arranged that the two line wires in multiple, with ground return, provide a telegraph circuit over which telegraph communication may be effected in both directions, without interference with the use of the line Wires in series for telephone or code signaling purposes. Heretoiore it has not been practicable to superimpose a telegraph circuit in this manner upon the line circuit of a central battery centralized traffic control system, such, for eX- ample, asthat shown in my prior application hereinbefore referred to, because the station apparatus is ordinarily'connected to the line wires in series andthe continuity of the line wires is at times interrupted bythe transmitting contacts at'the eld stations. Nevertheless, the C. T. C.

circuit energized `'from a central batteryat the control office is often preferred over the alternative bridged` line circuit as 'used heretofore in ycertain remote control systems, for the reason that sources of line current at the field stations are not required.L1

One object of the present invention is the provision Vof novel circuit arrangements for a central battery C. T. C. system, by means of which impulse codes may be transmitted from a control oice to various eld stations and from the 'stations to theoiice, over line wires arranged to provide at substantially all' times an uninterf ;rupted metallic circuit from end to end, which may be used for telephone and telegraph purposes, without interference; These arrangements include means' for signaling in one direction over the line wires by periodically discon- -nect'ing tlie source of current by which the line wires are normally energized at one end, and for signaling inthe opposite direction by periodicallyconnecting the line wires together through a suitable impedance, at the opposite end of the line or atan intermediate point, to vary the currentsupplied by said source.

Another object of my invention is the provision of a .system in" which 'current of one polarity is used for the transmission of control codes from the'oi'ce, and the 'opposite polarity is used both for the transmissionv of indication codes from the stations and vof selector codes from the oiice, without interference.

. Anotherf object is the provision of animproved lockout circuit for insuring thatl when two or :,each stationtransmitter after having transmittedv the first impulse'A of a code until a return impulse is received from the oilice of a character indicating that theofce apparatus is in condition Yto receive the'code. y l

Stillanother vrfeatureof my invention is the provisionV of 'a Wheatstone bridge circuit at each station which is lfornfied by the operation of the station transmitter, and which is effective to reduce the potential diierence across the, line Wires extending to stations more remote from'the oiiice subs'tantially tor zerovwhile maintaining a substantiallp'tential,difference across the 'line Wires extending" toward the oice to' effect the selective energzation of relays' at, the ystations in accordance with their relative locations With respect ton the office.

Other objects, purposes and features of my invention will be pointed out as the description proceeds.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the specific embodiment of my invention illustrated in the accompanying drawing', it is to be understood that the centralized traiic control system chosen to illustrate my invention is the Time code system of the Lewis application, Serial No. 600,786, corresponding to British Patent No. 415,787, while the selector system is that of the Field Patent No. 1,343,256, granted June 15, 1920, each of which systems as herein disclosed having been modied in certain respects in accordance with the requirements of my invention as will hereinafter be pointed out.

To facilitate an understanding of myinvention I have designated those elements of the C. T. C. system shown in the accompanying drawing which are similar to corresponding elements of the system of the Lewis British patent, such as the master relays M, the transmitter relays T, the slow-acting relays L, etc. by the same ref-V erence characters as employed in that patent, and likewise in respect to the-selector system shown herein, it is to be understood that the code wheel 89, contacts 96 and 91, relays 86 and 87,- and the selector 12 are similar to the correspondingly designated devices of the Field patent referred to.

As explained in the British patent, the reference characters Y and Z designate the line wires' of the system which extend fromthe point of control, usually a train dispatchers oice, as indicated by the legend Ofiice on the drawing; through each of a plurality of iield stations of the C. T. C. and selector systems in turn, the successive sections of the line :being distinguished by numerical suixes. Since the C. T. C. eld stations are generally similar, and since the selector locations are also similar one to another, only one of each is shown in order to simplify the drawing. The line wires Y and Z are included in a normally closed line circuit energized from a central battery 80 at the office which includes the normally closed contacts of a transmitter relay OT and the windings of two line relays ORC' and ORI at the oflice, the winding of a line relay RC at each C. T. C. eld station and the winding of a line relay SR at each selector location. The line relays shown herein are to be understood to be of a sensitivebiased polar type each having two balanced line windings of relatively low impedance such as are employed in the system of my prior application, Serial No. 256,976, while relays ORC and ORI each have, in addition, a third winding by means of which they may be biased electrically and thereby rendered responsive to variations in the strength of line current ofthe proper polarity.

Each line relay is biased to the right, as indicated conventional-ly by a tension spring attached to its armature, and therefore closes its righthand contacts when deenergized, and it is to be understood that each line relay isso polarized that the flow of current through any one of its windings when the positive terminal of the source is connected to the left-hand terminal of the winding will operate the armature in opposition to the bias to cause the left-hand contacts to be closed. The direction of the current normally flowing through the windings is indicated by arrows on the drawing. l f

This normally closed C. T. C. line circuit as shown in the drawing may be traced from the upper or positive terminal of battery 80, resistor 5, contact 6 of transmitter relay OT, normal contact 'I of a stick polar relay PC, back contact 8 of relay 86, through the upper windings of a low-pass lter comprising coils 9 and condensers IE), the upper windings of relays ORC and ORI to line Y, thence over back contact 30 of relay T through the upper winding of relay RC to the line wire sections YI and Y2, the upper winding of relay SR, line wire Y3, the upper winding of a telephone transformer or repeating coil II, resistor I 2 to wire XI. From this point the current returns to the lower terminal of battery 8U over a precisely similar path which as will be clear from the ldrawing includes resistor I3, the lower windings of the repeating coil II and of the line relays, the several sections of line Z, and contacts I4, I5 and I6a of relays 86, PS and OT. Relay RC is normally energized, as shown, like the station line relay R of the British patent hereinbelow referred to, and functions like that relay to hold the station coding unit of the C. T. C. system in its normal inactive condition.

The oice line relay ORC, however, occupies its deenergized position lbecause the eiect of the line current is balanced or neutralized by an opposing current iiowing from the upper terminal of battery 80, resistor 5, resistor or articial line I9, back contact 20 of relay OM, through the middle or local windings of relays ORI and ORC to the lower terminal of battery 80. Relays ORI and SR normally are held in their deenergized positions by the reverse current in their windings as well as by their bias. The station line relays RI are normally -deenergized The office coding unit is controlled by one 0r the other of the two line relays ORC and ORI, dependent upon the position of relay OM, over two wires I'I and I 8 which correspond to the two wires leading to terminal B of a source of current over the front and back contacts, respectively, of the office line relay OR of the British patent.

The circuits by which the timing relays OLI, OLZ, etc., are controlled over wires I'I and I8 are similar to the corresponding circuits shown in the patent, 'being reproduced herein merely for convenience. This is also true of the station circuits for controlling the relays LI, L2, etc. As shown herein, terminal B of the local source is normally connected to wire I'I over back contact 2i of relay OM and right-hand contact 22 of relay ORI. The oce coding unit is therefore held normally in its inactive condition as in the system of the patent.

The C. T. C. and selector systems are interlocked so that but one can obtain the use ofthe line at a time, by including back contacts of relays of each system, which open when the system is in use, in the starting circuits for the other system, as will hereinafter be explained.

I shall now describe the operation of the C. T. C. system in detail, rst explaining the transmission of a control code from the office, and then the transmission of an indication code from a eld station. The operation of the selector system will then be described, and iinally the operation of the superimposed telephone and telegraph circuits will be explained.

With the selector system in its normal inactive condition, as shown, it will be assumed that the operator initiates a C. T. C. control code by positioning suitable control levers and then picking up a start relay to energize the master relay asaoss' OM as explained in thev Lewis British patent. The picking up of a relay start as shown herein completes a pick-up circuit at its contact 23 for relay OM, which circuit, as in the patent, includes back contacts b of the slow-acting relays OLi or OL2, one or the other of which is energized when the line is in use, the circuit as shown herein extending to terminal B of the local source at back contact 2li of relay BS. Relay OM therefore picks up, and by opening contact 20 interrupts the circuit through the local windings of the line relays ORC' and ORI. The direction of current 'through the line winding of relay ORI is such that this relay remains in its deenergized position as shown, but relay ORC is now conditioned to respond to the normal line current and therefore operates its contact' 25 to the left. Contacts 2|, 2S and 2l ofrelay OM operate to transfer the control of the oice coding unit from relay ORI to ORC, wire Il now being energized from terminal B over the front or left-hand contact 25 of relay ORC and front contact 2S of relay OM, and wire I8 becoming energized over right-hand contact 25 Whenever relay ORC is released during the transmission of the control code. The condition of the apparatus controlled over wires Il and IB is now precisely as in the system of the British patent hereinbefore referred to, and ,therefore operates as therein described. For an understanding of my invention it is believed sufficient to point out that relay OT operates intermittently to deliver a code of impulses and intervals of selected lengths to the line to which relays ORC at the odce and relay RC at each C. T. C. station respond. The coding apparatus responds selectively to pick up a selector relay such as relay 23QS at the office and a selector relay S at the corresponding station in accordance with the character of a first portion of the code, and then other relays controlled by relay S are governed in accordance with the positions of control levers associated with relay 2315s. The first interruption of the line circuit completes a pick-up circuit from terminal B over the right-hand contact 25 of relay ORC and front contact 2l of relay OM, wire I8, back contact d of relay OLBP, back contact f of relay CL2, back contact b of relay OLB?, relay OLI to terminal C, so that relay OLI picks up, closing a branch circuit over its contact a from wire I8 through relay OLE to terminal C so that relay CL2 picks up. The closing of contacts c of relays OLI and OLZ completes a circuit for relay OLB; which picks up, closing in turn its contact c to pick up relay OLBP. The latter relay, at its contact b, transfers the control of relay OLI to wire I'I so that, during the transmission of the code, relay OLI is energized each time relay ORC picks up, and relay OL?. is energized each time relay ORC releases. If the line fails and remains open during transmission, it will be seen that relays OLI, OLB and OLBP will release successively, relay OLB at its contact a` opening the stick circuit including the winding and front contact a of relay OM Iby which relay OM is held energized to maintain the transmitter in operation, but relay OL2 will be held energized over wire I8 and its front Contact a. It follows that if the line fails, transmission is stopped, and that the starting circuit does not become available until the line is again restored, all of which is precisely as described in the British patent.

At the end of the control code, the operation of relay OT ceases and the line becomes steadily energized, whereupon relaysOLQ', OLB,

order. Relay OM uponireleasing transfers'the connection from terminal B to wire II over the front contact of relay ORC to the branch circuit including the right-hand or back contact 22 of relay ORI, and-by closing contact 20 reenergizes the local windings of the oice line relays, so that relay ORC becoming balanced, assumes its deenergized position, thereby `restoring the apparatus to its normal condition, as shown.

At the eld station, wire 'I3 corresponding tol RC. Since relay RC is in series with relay ORC,`

it will be seen that wires'IS and 'Il are'energized infunisonwith wires I'I and IB'of the omce coding unit andtherefore thestation slow acting relays Ll, L2, LB and LBPVare each operated inv unison with the correspondingofice relay and that the station apparatus Vwill'selectively receive the control code as described inl the British patent.

I shall next assume that a station device having indications to transmit changes its conditionr thereby` energizing the station starting relay ST. When the line assumes its normal condition after the transmission of the control code as already described, relays L2 and LI release, and a starting circuit is completed from terminal B at contact c of relay ST as describedin the patent to pick up relay M, which in turn picks up relay T to initiate the first step of an indication code.

In the system of the patent, relay T operates like relay OT already described to open the line circuit, but as disclosed herein, the transmission is eifectedin a novel manner which maintains the continuity of the line wires from one end of the line to the other, thereby avoiding interference with the telephone or telegraph circuits When relay 'I' picks up, ie line wires Y and Z are connected together through the windings of relays RI and RC, insuch a manner as to f orm a Wheatstone bridge comprising two'branches each shunting the wires Y and Z but so balanced that wires YI and ZI leading to more remote stations are brought to the same potential, thereby reducing the current in the portion of the line circuit lextending to the more remote stations substantially to zero. This portion of the line circuit includes resistors I2 and I3 which are customarily of 500 or 1000 ohms each and its resistance its relatively high in comparison with that lof relays RI and RC, which are normally 5 or l0 ohms per winding. It follows that due to the shunt paths provided through relays RI and RC when relay T is picked up, the resistance of the remaining portion of the line circuit is substantially reduced, thereby increasing the current through the ofce line relays, so that relay ORC picks up.

One branch of the Wheatstonc bridge referred to may be traced from wire Y, front contact 30 of relay T, the upper winding of relay RI, the right-hand winding of the choke coil 3l, to wire ZI, and from Wire ZI through the lower winding 0f relay RC, resisto-r or artificial line 32 to wire Z. The other branch of the brid-ge may be traced from wire Y, resistor or artificial line 33, the upper winding of relay RC to wire YI, and from wire YI through the left-hand winding of coil 3| 'l andthe lower-"winding of relay RI, front conv OM, OLBPand OLI release successively, in that tact 34 of relay 'I to wire Z. Since the two branches include similar elements, it is evident they may readily be balanced to bring points YI and ZI to the same potential. It will also be seen that the shunt paths from wire Y to wire Z have the characteristics of a low pass filter such as the one comprising the coils 9 and condensers I at the oiiice, since they include the series coils 3| and shunt elements comprising the condensers 35 in the line and the condensers 36 bridging the contacts of relay T.

In the system of the British patent, the rst step of an indication code is a short line open step, while the first step of a control code is made relatively long in order to give precedence to the control code in the event the office and one or more stations initiate codes at the same time. In accordance with my invention this diierentiation is obtained in a dilerent manner, consequently, the station transmitter T may be arranged to function on the rst step in the same manner as the oice transmitter OT. It is there.

fore to be understood that relay T remains picked up on the rst step for a relatively long time interval. The line relays RC at the more remote stations therefore receive a long line open code step due to wires YI and ZI being held at the same potential by relay T at the transmitting station, the same as when a control code is being received, and the relay E of the station coding unit which responds selectively to a long rst step picks up at each of these more remote stations to open at its contact athe energizing circuits for the associated relay M, just as when the line is sectionalized as occurs under corresponding conditions in the line circuit of the patent.

It will be clear therefore, that when indication codes are initiated by two or more stations at the same time, the station nearest the oliice retains sole control of the line, as heretofore.

When the oiice line relay ORC picks up due to the increase in line current produced by the station relay T, it completes a circuit from terminal B at its left-hand contact 25, back contact 26 of relay OM, back contact 31 of relay OLBP, the upper winding of relay PC to terminal C. Relay PC is a polar relay of the magnetic stick type and now operates its contacts 'I and I5 to the left, to reverse the polarity of the current supplied by battery 80 to the line circuit, and removing relay OT from control of the line.

At the transmitting station, due to the reversal of the polarity of the line current, relay RI picks up and relay RC releases, completing a circuit from terminal B over contacts 38, 39 and 40 of relays RI, RC and M, through relay MP to terminal C, and relay MP picks up to complete a stick circuit extending to terminal B at its front contact 4I.

'I'he station coding apparatus at the transmitting station does not respond to the initial energization of relay T but is held in its normal inactive condition until relay RC releases, whereupon wire I3 is deenergized and wire TI becomes energized over the right-hand contact 29 of relay RC, and as soon as relay lvIP picks up, contact 29 is disconnected and terminal B is connected to wire TI over front contacts 28 and 42 of relays MP and RI. Relay MP opens contact 43 in the circuit for relay E, so that relay E remains deenergized at the transmitting station.

It will be seen that if the oice and one or more stations are conditioned to start transmission at substantially the same time, the station nearest the ofce will retain control of the line only if it succeeds in reversing relay PC, and otherwise the oilce will retain control of the line, but in any case the selection is obtained in a positive manner because it depends merely upon the position of relay PC. In the event relay OM picks up, relay PC will fail to reverse in response to the initial energization of the station transmitter relay T, and the opening of the line circuit by the oflice transmitter OT will release relay RC without energizing relay RI thereby energizing wire 'II and eventually picking up relay E at the transmitting station to release relay M at that station. It will be seen that under these circumstances the system functions precisely as when the line circuit of the patent is used, in that all the stations are conditioned to receive the control code.

Assuming that a field station retains control of the line, when the line polarity is reversed by relay PC, the cnice line relay ORC releases and relay ORI picks up to close its left-hand contact 22. The balance due to the current through the local windings of these relays which with normal polarity is eiective to govern relay ORC is now effective to govern relay ORI, which therefore picks up when relay T picks up to shunt the line wires through relays RI and RC as hereinbefore described.

It follows that relays ORI and RI pick up on each odd numbered step of the code, when relay T is picked up, and release on each even numbered step, when relay T releases. In other words, in an indication code, the increase in line current, due to the shunt applied to the line at the transmitting station for energizing relays ORI and RI, corresponds to a line open step of a control code, and the restoration of the line to normal by removing the shunt to release relays ORI and RI, to a line closed step of a control code.

It will be evident without further explanation that the 'continued operation of relay T will result in the proper transmission of an indication code. As described in the British patent, relay OIG at the oilice, and relay I6 at the station, become energized on the sixteenth or final step of an indication code. Relay I6 by opening its front contact c releases relay M to stop the operation of relay T, while relay OIG, as shown herein, closes a Contact 44 to momentarily energize the lower winding of relay PC in such a direction as to cause contacts 'I and I5 to move to the right, thereby restoring the line circuit to normal. At this time, relay T is deenergized, consequently ORI is balanced and relay ORC energized in such a direction as to close its righthand contact 25. Consequently both these relays occupy their normal positions as shown in the drawing and remain in that position after the line polarity is restored to normal. At the transmitting station, relay RI is deenergized and relay RC energized in such a direction as to close its right hand contacts 29 and 39, relay RC having been held in that position forthe duration of the indication code. When the line polarity is restored to normal, relay RI being disconnected remains deenergized but relay RC picks up closing its left-hand contacts 29 and 39. W'lien relay Mvreleases on the last step, the release of relay MP follows, transferring the energization of wire 'I3 from contact 42 to contact 29 so that wire 'I3 remains energized. Then relays L2, LB, LBP, I6 and LI release successively in that order, completing the restoration of the station apparatus to normal.

kThe selector transmitting apparatus, asex-l plained in the Field patent, comprises a plurality of code wheels B9, one for each selector, of Which but one is shown herein, each of which when wound up and released makes one revolution during which a connecting relay 85 is energized to permit a code transmitter relay'l to function. As the code wheel rotates, relay 81 is intermittently energized over a circuit including the code wheel contacts 96 and Sl in accordance with the arrangement of the code wheel teeth, to deliver a code of direct current impulses, all of which are of the reverse polarity, to the line wires Y and Z for operating the line relays SR.

As disclosed herein, the apparatus is arranged so that the operation of a code wheel is ineffective unless it is released when the line is available, as manifested by the deenergized condition of the relays OM, OL2 and OLI of the C. T. C. office coding unit. When these relays are all de- .energized, the release of a code wheel completes a circuit from terminal B over the back contacts 45, 48 and lil of these relays, back contact 48 of relay 8B, code wheel 89, contact 96 and relay 8S to terminal C. Relay. 88 picks up to connect the l line wires Z and Y to battery 83 over its front contacts i4 and 8, and contacts 3 and 4 of relay 8l, and at its front contact i9 completes a stick circuit for itself which is independent of the relays OM, OLE and OLI and which is opened at contact 95 when the code wheel 8S completes its revolution. The circuit for intermittently Venergizing the code transmitter relay 81 extends from terminal B, contacts its and 53, code wheel 89, contacts St and Si, relay 81 to terminal C'.

It is to be noted that as shown herein relay Sl has front contacts only, and that the selector codes include impulses of only one polarity while in the Field patent it is employed asa pole changer to deliver impulses of alternately opposite polarity to the selectors l2, these being bridged directly across the line in series with a condenser lli. As shown herein each selector 'I2 is energized through its condenser 74, by irnpulses of alternately opposite polarity generated locally in response to the operation of its associated line relay SR, as will be apparentjfrom the drawing.

During the transmission of a selector code by relay 8l, the C. T. C. ofce transmitter is prevented from functioning because the .pick-up circuit forrelay OM is held open at back contact 24 of relay B. Since the selector code irnpulses are all of the reverse polarity, it is evident thatthe C. T.'C. station relays RC will remain in r theirY deenergized position. Each relay L2 is therefore held energized. over wire I'I and its front Contact a, and holds its baci; contact b` I open in the pick-up circuit for the. associated relay M to prevent'the station transmitter from functioning. At the odios, relays CRC and ORI remain in their deenergizcd positions during the transmission of the selector codes, andit follows that the T. C. receivers at the office and stations are wholly non-responsive to the .sen lector codes. Y

It will be evident that theselector line relays SR are non-responsivcto ,control codes, and are also non-responsive to indication codes provided the Vrelay SR is located between the office and the transmitting station, and will respond to an indication code only when located at a.

point more remote from the ofce. It is'however, impossible to operate any selector by a C. T. C. c-ode because of the difference in .code f character. As-described :in the Field patent,- the selector code includestwoflong steps in a code of 32 steps or less, the total number of steps chosen for illustratonbeing 15, although in present day practice, a total of 17 or 2-7steps is generally used. The selectors Iare immune 'to the C. T. C. ,codes because the lattercodes 'always contain atleast i'three long steps and the number of short impulses in any'l'l consecutive steps is insufficient to advance a selector to the point required to close its final Contact. t follows that the total number of codes provided by both systems may be used vwithout interference.

As hereinbefore mentioned, the line wires Y and Z provide a non-interfering telephone circuit which as shown extends from the telephone apparatus 5E) at the ofiice through a high-pass filter illustrated as the condensers 5I to line wires Y and Z, thence from station to station through ythe by-pass condensers 35 bridging the line relays RC and condensers 52 bridging the line relays SR, andr through therepeating coil II to the telephone apparatus at kthe distant end of the line.

At the office, the C. T. C. and selector apparatus are connected to the line wires Y and Z through a conventional low-pass ltercorree sponding to that of the Field patent and :comprising coils 9 and condensers I0, which effectively prevents the shunting of the telephone currents through -battery 8D, and at the same time limits the `rate ofjchange of the code signaling currents to render the control and selector codes substantially inaudible in the telephones. The y NI or Bl, thecontacts of a pole-changer relay PC I, and the balanced windings of a line relay RI to line X 0-r XI and through an articialline AL to ground. VThe line wires Y and Z complete a metallic connection between Vwires X and XI by the provision of ther usual simplex connection at each end. As illustrated, wire X is connected .to

wires Yand Z at lone end of the line through resistors-54 and A55V, the coils 9 and the windings of the oi'ce line relays, while wire XI is connected `to Y and Z `at the other 'end ofthe line through resistors I2 and I3 andv the .repeating coil yI I.

thewinding's of the line relays they are without effect upon the C. T.l C. or selector systems, and it isalso obvious thatrthe resistorsV I2, I3, 54 and 55 may be readily balanced so that no current from battery 8D flows through the telegraph lrelays RI.y .The two windings of each voi" the filter coils 9 and '3l arey preferablyiclosely coupled so as to `present the minimum impedanceto the telegraph currents flowing in oppositedirections through these windings. The telegraph circuit moreover is not 'eiected by the operation of the station transmitter T. Normally, the telegraph currents pass from wires Y and Z to wires'YI and ZIover the back contacts and 34 of'relay T and therwindings of relayRC. When relay T Since the telegraph currents in linev wires Y and Z ow in opposite directions through.

pleted from wires Y and Z over the front contacts 30 and 34 and the windings of relay RI and coil 3| to wires ZI and YI, respectively, so that when the bridge which these circuits form is balanced the resistance with respect to the telegraph currents is the same with relay T picked up as when relay T is released, and the transmission of indication codes is therefore without eiect upon the telegraph circuit.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In a remote control system, an oiiice and a station connected by two line wires, a normally closed signaling circuit including said line wires and a source of current, line relay means at the office responsive to a substantial increase in current in said line circuit, a code transmitter at said station operable to connect said line wires together at the station to increase the current in said line circuit repeatedly in accordance with a code, and a code receiver at the oflice governed by said line relay means and selectively responsive to said code.

2.` In a remote control system, an oce and a station connected by two line wires, a normally closed code signaling circuitincluding a source of current at the oice and said line wires in series, a line relay at the office responsive to variations in current in said line circuit, a superimposed signaling circuit including said line wires in multiple, a code transmitter at said station operable to connect said line wires together to vary the current in said normally closed circuit repeatedly in accordance with a-code while maintaining the continuity of said superimposed circuit, and code responsive means controlled by said line relay selectively responsive to said code.

3. In a remote control system, an oflice and a station connected by vtwo line wires arranged to provide a voice frequency communication circuit, a code signaling circuit including said line wires in series and a source of direct current at the oice, lsaid sourcel being bridged across said line wires in series with a low-pass lter and a line relay, a code transmitter at said station effective when operated to connect said line Wires together through a low-pass lter to vary the direct current ilow in said code signaling circuit While maintaining the impedance of said voice frequency circuit substantially unchanged, and code responsive meansY at the oiice controlled by said line relay in response to said current variation.

4. In a remote control system, an office and a plurality ci stations connected by two line wires, a normally closed code signaling circuit including a source of current at said office, said line wires in series, and a relatively high resistance at the end remote from said office, a line relay at the oilice responsive to a substantial increase in current in said line circuit, a line relay at each station normally energized by the current in said line circuit, a code transmitter at each station operable repeatedly in accordance with a code and eiective when operated to connect said line wires together to increase the current in the line circuit portion between the oflice and said station and to reduce the current in the remaining portion substantially to zero While maintaining the continuity of said line circuit, code responsive means at the omce selectively controlled by the oflice line relay, and a starting circuit at each station for initiating the operation of the associated transmitter including a contact which opens if the line relay at such station becomes deenergized.

5. In a remote control system, an oice and a station connected by two line wires, a normally closed signaling circuit including a source of current at said oflice, said line wires, and a relatively high resistance at a point remote from said oice; line relay means at the oilice responsive to a substantial increase in the current in said line circuit, a code transmitter at said station o-perable to lbridge a relatively low resistance across said line wires repeatedly in accordance with a code to govern said line relay means, and a code receiver controlled by said line relay means selectively responsive to said code.

6. In a remote control system, an oiiice and a station, a simplexed telephone line comprising two line wires connected in series to telephone apparatus and in multiple to telegraph apparatus at each end to provide simultaneously available telephone and telegraph circuits for communication between the two ends of said line, a normally closed code signaling circuit including said line wires in series and a source of direct current at the oiiice, said source being bridged across said line wires in series with a low-pass filter and a line relay balanced with respect to said telegraph circuit, a code transmitter at said station operable to connect the line wires together through a low-pass lter to control the line relay in said code signaling circuit while maintaining the impedance of said telephone circuit and also of said telegraph circuit substantially unchanged, and a fcode receiver at the office controlled by said line relay.

'7. In a remote control system, two line wires extending from a central oiiice through an intermediate station to a more distant station, a normally closed code signaling circuit including, in

r series, a source of current and line relay means at said oi'lce, said line wires and a resistance connecting said line wires at said more distant station; a local balancing circuit effective to neutralize the eiect upon said line relay means of the current normally flowing in said code signaling circuit, -but rendering said line relay means responsive to an increase in said current, a code transmitter at the intermediate station operable to close a relatively low resistance bridge across said line wires repeatedly in accordance with a code to govern said line relay means, and a code receiver controlled by said line relay means selectively responsive to said code. n

8. In a remote control system, two line wires extending from a central oilice through an intermediate station to a more distant station, a normally closed line circuit including in series a source of current at said office, said line wires and a normally energized line relay at each station; line relay means at the oflice responsive to a substantial increase in the current in said line circuit, a code transmitter at each station eiective when operated to shunt said line circuit to increase the current in the portion thereof extending to the oilice and to decrease the current in the remaining portion substantially to zero, each said transmitter when initiated being operable repeatedly in accordance with a multiple step code to govern said line relay means, a code receiver controlled by said line relay means selectively responsive to said codes, and means for 'more distant station; a second impedance bridged across said line Wires at said oflice, a superimposed circuit extending rom the mid-.point of one said impedance to the mid-point of the otherand including said line wires in mutliple, `line relay means at the oce responsive to a substantial increase in the current in said code signaling circuit but balanced with respect to said superimposed circuit, a code transmitter at each station eiective when operated to .complete a Wheatstone bridge circuit forming a shunt effective, to

increase tne current in the portion of thecode signaling circuit extending to the oice, said bridge being balanced to reduce the current in the remaining portion of said circuit substantially to zero While maintaining the impedance of, .Said superimposed circuit substantially miclilanged, each said code transmitter when initiated being operable repeatedly in accordance with amultiple step code to govern said line relay means, axcode receiver controlled 4by said` linerelay means selectively responsive to said codes, and means for initiating each code transmitter V eective only when the associated line relay has ,beensteadily energized for a predetermined time interyal.

10Q In a remote control system, two line Wires exm tending from a central ofce throughanintermediate station to a more distant station, a norma closed code signaling circuit including, in series,

a source of current, line relay meansand a code transmitting Contact at saidoi'lice, Saidlline Wires, i

and a line relay at each station, a local balancing circuit eieotive to neutralize the eiectuponsalid line relay means of the current normally flowing in said signaling circuit, but rendering said line relay means responsive to a substantial increase in said current, means vfor at times opening Asaid local circuit to render said line relay means responsive to the normal current in said .signaling circuit and to initiate the operation of apparatus governed by said line relay means for repeatedly opening said transmitting contact to control said line relay means and said station relays in accordance With different control codes, code receivers controlled by the station line relays selectively responsive to said codes, a code transmitter at each station; means effectiveto initiate the` operation of each code transmitter effective at times provided said line circuit `has, been in its normal closed condition with said line relay Vmeans in its balanced condition for a predetermined time into val, means controlled by each code transmitter Y when initiated to repeatedly shunt said line Wires to increase the normal current in said line circuit to govern said line relaymeans in accordance with a code, and a codereceiver controlled kbysaid line relay means selectively responsive to each such code.

11. In a remote control system, two vline wires extending from a central oflice to a distant station, a normally closed line circuit including, in series, a source of current and a normally closed transmitting contact at said ocasaid line wires, and a normally energized line relay at said station; line relay means at the oiice controlled said line circuit, a code transmitter at said station efective when operated to shunt said'line circuit to increase the current in the portion thereof extending to the office, said transmitter when initiated being operable repeatedly inaccordance With a multiple step code to govern said line relay means, a code receiver controlled by said line relay means selectively responsive to said code, means for initiating said code transmitter effective only when the station'line relay is steadily energized, Vmeans at the` oiiice eiective at times for temporarily rendering said line relay means responsive to the normal currentv in ,said line circuit and for then operating said transmitting contact to repeatedly interrupt said circuit in accordance with diierent codes under the control of said line relay means, and a code receiver controlled by the station line relay selecf tively responsive to said codes.

12. In a remote control system, two line Wires extending from a central oice to a distant station, a normally Vclosed line circuit including, in series, a source of current of reversible polarity at the oiice, said line Wires, and a normallyv energized line relay `at said station; line relay means at the ofce controlled over said line circuit but normally responsive only to a substantial increase in current of normal polarity in said line circuit,

a code transmitter at said station effective when operated to Vshunt said line circuit to increase the current in the portion thereof extending to the olce, means for initially operating ysaid code transmitter eiective only when the station line relay is steadily energized to effectan initial operation oi said line relay means, means controlled plurality of stations, a Anormally closed Y,line 4circuit including in series, a source of current ,of reversiblek polarity at the ofoe, ,said `line Wires, and a normally energized line-relay responsive only to current of .normal polarity at each `station; linerelay means at the oicecontrolled over said line circuitbutnormally responsive only, to

a substantial increase in current ,ci normal polarity in said line circuit, a code transmitter vat each stationeffective Whenmoperated toclosea shunt across said line circuit to increase the curlrent in the portion thereof extending from such station to theV oiiice to operate said line relay means and to reduce the current inthe remaining portion extending tomore distant stations a substantially to zero", means efectiveonlycwhen a station `line relay is energized to, operate the associated code `transmitter for a predetermined time intervaLmeans controlled yby theline Vrelay means in response tosuch initial operation to reverse the polarity-of said'jcurrent, meansfat each station responsive only to current of reverse i polarity received .Within said predetermined, time interval after the initiation of the4 associated transmitter eective to4 refoperate4 said trans.-Y

rnitter repeatedly totransmit a multiple Vstep two line; wires code, a code receiver at the oilice selectively responsive to each said code, and means controlled by said code receiver for restoring the polarity of the line current to normal at the end of each such code.

14. In a remote control system, ltwo line wires extending from a control office serially through a plurality of stations, a code signaling circuit includingr said line Wires and a source of current of reversible polarity at the oice connected across said line Wires in series with a line relay biased normally to i-ts released position, a code transmitter at each station effective when operated to close a shunt connecting said line Wires to effect the operation of the omce line relay and to prevent the iiow of current in the portion of said line circuit extending from such station to stations more distant from the o-iice, means for initially operating each code transmitter for a predetermined time interval,v means controlled by the oilice line relay in response to such initial operation to reverse the polarity of the current supplied to said line Wires, means at each station responsive only to current of reverse polarity received Within said predetermined time interval after the initiation of the associated transmitter to re-opera-te said transmitter repeatedly to transmit a multiple step code, a code receiver at the oiiice selectively responsive to each such code, and means for restoring the polarity of the current supplied to the line Wires to normal at the end of each such code.

l5. In a remote control system, two line wires extending from a control oice serially through a plurality of stations, a code signaling circuit including said line Wires and a source of current of reversible polarity at the oice connected across said line Wires in series with a line relay biased normally to its released position, a code transmitter at each station eiective when operated to close a shunt connecting said line Wires to eilect the operation of the oiiice line relay and to prevent the flow of current in the portion of said line circuit extending from such station to stations more distant from the oiiice, a line relay at each station responsive only to current of reverse polarity included in the shunt at such station, means for initially operating each code transmitter for a predetermined time interval, means controlled by the oilice line relay in response to such initial operation to reverse the polarity of the line current, means effective only if the station line relay picks up within said predetermined time interval after the initiation of the associated transmitter to re-operate said transmitter repeatedly to transmit amultiple step code, a code receiver at the oice selectively responsive to each such code, and means for restoring the polarity of the line current to normal at the end of each such code.

16. In a remote control system, two line wires extending from a central office serially through a plurality of stations, a normally closed line circuit including, in series, a source of current of reversible polarity and a line relay biased normally to its released position at the oiiice, said line Wires, and a rst line relay responsive only to current of normal polarity at each staf tion, a code transmitter at each station effective when operated to close a shunt connecting said line Wires to effect the. operation of the oiiice line relay and to release the line relay at each station more distant from the office; a second line relay at each station responsive only to current of reverse polarity included in the shunt at such station, means at each station for initiating the operation of the code transmitter at such station provided the first line relay at such station is energized, means for maintaining each initiated code transmitter in its initial operated condition for a predetermined time interval, means responsive to the initial operation of the oiiice line relay for reversing the polarity of the line current, means for repeatedly operating each initiated code transmitter eiective only if the second line relay at the same station picks up Within said predetermined time interval, to transmit a multiple step code, a code receiver at the' office selectively responsive to each such code, and means for restoring the polarity of the line current to normal at the end of each such code.

17. In a remote control system, an ofce and a station. connected by two line wires, a normally closed signaling circuit including said line Wires and a source of current of reversible polarity at the ofce, a normally energized line relay at the station responsive only to current of normal polarity included in said circuit, a line relay at the oiiice biased normally to its released position included in said circuit, a code transmitter effective when operated to connect said line wires together at the station .to increase the current in said line Wires to operate the oflice line relay, means eiective only when the station line relay is energized for initiating the operation of said code transmitter, means controlled by the oiiice line relay in response to such initial operation to reverse the polarity of the line current, means at the station responsive only to line current of reverse polarity of re-operating said transmitter repeatedly to transmit a multiple step code, a code receiver at ythe oiiice selectively responsive to said code, and means for restoring the polarity of the line current to normal at the end of said code.

18. In a remote control system, an oice and a station connected by two line wires, a line circuit including said line Wires and a source of current of reversible polarity at said oii'ice, a line relay at the oiice biased normally to its released position included in said line circuit, a code transmitter effective when operated to connect said line Wires together at the station to increase the current in said line circuit, means for initially operating said code transmitter, means at the oifice responsive to such initial operation to reverse the polarity of the line current, means at the station responsive only to current of reverse polarity for re-operating said transmitter repeatedly in accordance With a code to operate said oiiice line relay, means controlled by said oilice line relay for selectively receiving said code, and means for restoring the polarity of the line current to normal at the end of such code.

19. In a remote control system, an oflice and a station connected by line Wires; a normally closed line circuit including a source of current of reversible polarity, a normally closed transmitting contact, and a line relay biased normally to its released position at the oilice, said line Wires, and a-normally energized line relay responsive only to current of normal polarity at said station; means at the ofiice for at times operating said transmitting contact repeatedly to open and close said line circuit in accordance with different multiple step codes, a code transmitter effective when operated to connect said line Wires together at the stations to increase the line current, means effective only when the station line relay is steadily energized for initially operating said code transmitter, means at the office responsive to such initial operation to reverse 'the polarity of the line current, means at the station responsive only to current of reverse polarity for re-operating said transmitter repeatedly in accordance with a code to govern said oiiice line relay, means for restoring the polarity of the line current to normal at the end of such code, and code receivers controlled by the ofce and station line relays, respectively, responsive to said codes.

20. In combination, an oice and a plurality of stations connected by two line Wires arranged to provide a continuous metallic communication circuit from one end to the other, a remote control system for transmitting multiple impulse codes in both directions between said office and stations over said line Wires While maintaining the continuity of said communication circuit comprising a source of current at the office normally supplying current to said line Wires, a code transmitter at the oice operable at times to periodically disconnect said source from the line wires to transmit codes to the stations, a code transmitter at each station operable when initiated to periodically connect the line Wires together to prevent the flow of current kto stations remote to the oice While increasing the current supplied to the line Wires to thereby transmit a code to the oiice, and means for initiating the operation of each code transmitter effective only When current is steadily being supplied over said line Wires to the corresponding station.

2l. In a remote control system, an oiiice and a station connected -by two line Wires, a sourcelof current of reversible polarity at the oiice connected to the line Wires and normally supplying current of normal polarity to said station, a code transmitter at the oilice effective when initiated to periodically disconnect said source from the line Wires to transmit multiple impulse codes to the station, means effective at times for initiating the omce transmitter, a code transmitter at the staton effective When current of reverse polarity is being supplied to the line wires to periodically increase said current to transmit multiple impulse codes tothe oiiice, and means for initiating said station transmitter comprising means at the oiiice responsive to the increase in line current due to an initial operation of said station transmitter occurring when the line Wires are Ibeing supplied steadily with current of normal polarity to reverse the polarity Vof said current. Y

22. In combination, an ofiice and a plurality of stations arranged in two groups connected by line Wires, a normally closed line circuit including a source of current at the oice, a normally closed transmitting contact, and said line wires; a biased polarized line relay at each station included in said line circuit, the line relays at the stations of one group being responsive only to current of the polarity normally supplied to said line circuit and those at the stations of the other group responsive only to current of the opposite polarity, means for operating said transmitting contact at times for controlling the line relays at the stations of said one group in accordance with a code of time spaced impulses all of normal polarity, means ior at times temporarily disconnecting said transmitting contact and for then supplying to the line circuit a code of time spaced impulses of current from said source all of the 4reverse polarity to which the line relays at the stations of the other group are responsive, and a code receiver selectively controlled by each line relay.

23. In combination, an oice and a plurality of stations connected by line wires providing a telephone circuit, a selector call system associated with said telephone circuit, a remote control system having a normally closed line circuit including said line Wires and a source of cur.- rent at said ofiice, and code receivers at one or more of said stations, a code transmitter at said oiiice operable only when said selector call system is inactive to control said line circuit to transmit codes from the oiiice to said stations comprising time spaced current impulses all of the same polarity for selectively controlling said receivers, and means for operating said selective call system eiective only when said code transmitter is inactive to transmit other codes to said stations comprising time spaced current impulses all of the opposite polarity, and selectors at certain of said stations controlled over said line circuit selectively responsive to said other codes.

GEORGE W. BAUGI-IliIAN. 

